1985 70hp Yamaha Revs to Full RPMs in Idle

[Gatorzone19]

The motor is a 1985 Yamaha 70hp. The problem is when I start the motor up it instantly revs up to high RPMs in neutral and doesn't stop. This started after I disconnected the fuel line from the motor for the first time in 6 months to clean the boat. When I connected the fuel line back to the motor it didnt seem like it connected all the way but it seemed to work. So I went out on the boat and was running about 25 mph when the motor bogged down and shut off. I couldnt get it started.(Im almost postive it was flooded). Waited a couple minutes then got it started and it instantly rev ved to very high rpms in neutral so I shut it off. I then started it again but put it into gear very quickly and it would die when going slow but if I brought it above crusing speed it would run fine and if I slowed down it would die again. I checked the gears and timing , everything seemed to be working fine. I also got a new "fuel line to tank connector" that connects to the engine perfectly. Somebody mentioned it might be something with the carbuerator. Any ideas why the engine is doing this and how can I fix it? Thanks

 

[SparkieBoat]

Re: 1985 70hp Yamaha Revs to Full RPMs in Idle

sounds like you may have a carb flooding..tilt your motor up and remove carb cover then pump bulb and look for fuel coming out of a carb..that would mean that you have a stuck needle valve

 

[Gatorzone19]

Re: 1985 70hp Yamaha Revs to Full RPMs in Idle

Disassembled the carbs today to clean them and look for a stuck needle valve. Nothing wrong from what I could see.(I dont know a ton about motors). Tomorrow I will start the motor up and see what happens. If I still have the problem, do you guys have any other ideas on what might be wrong?

 

[99yam40]

Re: 1985 70hp Yamaha Revs to Full RPMs in Idle

To rev up like that something would need to be opening the butterflies on the carbs to let more air into the motor and /or the timing would be advanced outside of where it should be at idle.
Check linkages.

 

[SparkieBoat]

Re: 1985 70hp Yamaha Revs to Full RPMs in Idle

did you pump the bulb and look for leaking first?? if needle valves are seating properly then your bulb should pump up tight. then check the things mentioned by 99

 

[robert graham]

Re: 1985 70hp Yamaha Revs to Full RPMs in Idle

Like 99yam40 says, it's almost got to be something sticking in your throttle linkages or controls. Remove cowl and check the carb area linkages for proper movement. Good Luck!

 

[Gatorzone19]

Re: 1985 70hp Yamaha Revs to Full RPMs in Idle

When I move the fast Idle lever should all the linkages on the carbs move?

 

[noelm]

Re: 1985 70hp Yamaha Revs to Full RPMs in Idle

a very high rev at idle does NOt always mean it is jammed open, an air leak or lack of fuel is very common too ,think what happens to your mower when it runs out of fuel, it revs like crazy! so make sure the mechanical side of it is OK, that is, the cable is not snapped or jammed and the htrottle is wide open, and then chase your problem, but do not just look for too much fuel, it can be either.

 

[99yam40]

Re: 1985 70hp Yamaha Revs to Full RPMs in Idle

When I move the fast Idle lever should all the linkages on the carbs move?

Yes all carb linkages should move in unison, but not very far with the idle lever